UHMWPE has a molecular weight of at least 1,000,000 Da, which is 10 to 100 times greater than the molecular weight of high-density polyethylene (HDPE). UHMWPE offers major advantages in increased impact resistance, tensile strength, abrasion resistance, and stress-crack resistance. UHMWPE can be produced by Ziegler polymerization. The process requires exceptionally pure ethylene and other raw materials. Like conventional HDPE, UHMWPE made by Ziegler polymerization has a broad molecular weight distribution Mw/Mn (Mw is the weight average molecular weight, Mn is the number average molecular weight) of within the range of 5 to 20.
However, UHMWPE with a narrow molecular weight distribution Mw/Mn of less than 5 have improved mechanical properties. Newly developed metallocene and single-site catalysts advantageously provide polyethylene and other polyolefins with very narrow molecular weight distribution (Mw/Mn from 1 to 5). The narrow molecular weight distribution results in reduced low molecular weight species and higher Mn which further improves abrasion resistance. These new catalysts also significantly enhance incorporation of long-chain a-olefin comonomers into polyethylene, and therefore reduce its density. Unfortunately, however, these catalysts produce polyethylene having a lower molecular weight than that made with Ziegler-Natta catalysts. It is extremely difficult to produce UHMWPE with conventional metallocene or single-site catalysts.
U.S. Pat. No. 6,174,976 discloses novel olefin polymerization catalysts based on neutral nickel complexes of bidentate ligands containing a nitrogen atom and an oxygen atom and a process for the preparation of polyolefins using such catalysts. Preferred ligands possess imine and carboxylate groups. A batch or continuous process for the preparation of polyolefins comprising contacting, at a temperature from about −100° C. to 200° C., one or more monomers of the formula R1CH═CHR2 with, (i) a compound of the formula I, (ii) a suitable nickel compound, and optionally, (iii) a neutral Lewis

PCT Appl. No. 2004052980 discloses compound suitable for use as a catalyst for ring opening polymerisation reactions for example for the polymerisation of lactones, lactides etc, the catalyst comprising the reaction product of (i) an alkoxide, halide, condensed alkoxide, amide, condensed amide, mixed halo-alkoxide or, mixed halo-amide, sulphonic acid derivative, sulphonamide, silanol or silylamide of titanium zirconium, hafnium or aluminium or a mixture thereof, and (ii) a complexing compound selected from the list comprising oximes, hydroxy-Schiff bases, 8-hydroxyquinoline derivatives, 10-hydroxybenzo-[h]-quinoline derivatives, hydrazones and substituted phenols. The catalyst composition is preferably of the following general formula Yn-(X.Z)-M-Lx where Y represents a monovalent ligand (such as alkoxy, amide, sulphonato or silanoxy), n represents the valency of the metal M, x is the no of moles of complexing compound associated with each metal atom and z is the number of covalent bonds formed between each L and the metal M. For example, the catalyst composition is represented by the following structural diagram:

Article titled “Olefin polymerization” reports olefin polymerisation by using methylaluminoxane (MAO).
Article titled “Aldehyde and ketones” reports the synthesis and mechanism for imine formation.
European patent 0874005 discloses olefin polymerization catalyst exhibiting excellent polymerization activities, a process for olefin polymerization using the catalyst, a novel transition metal compound useful for the catalyst, and an α-olefin/conjugated diene copolymer having specific properties. The olefin polymerization catalyst of the invention comprises (A) a transition metal compound of formula (I), and (B) an organometallic compound, an organoaluminum oxy-compound or an ionizing ionic compound. The novel transition metal compound of the invention is a compound of formula (I) wherein M is a transition metal atom of Group 3 or 4 of the periodic table; m is an integer of 1 to 3; R1 is a hydrocarbon group, etc.; R2 to R5 are each H, a halogen, a hydrocarbon group, etc.; R6 is a halogen, a hydrocarbon group, etc.; n is a number satisfying a valence of M; and X is a halogen, a hydrocarbon group, etc.

PCT Appl. No. 2013020896 discloses Group 4 transition metal complexes of bidentate iminonaphthol pro-ligands are claimed. These can be used as catalysts to polymerise olefins, preferably ethylene, inter alia to prepare ultra high molecular weight polyethylene having a narrow molecular weight distribution, due to the single-site nature of the catalyst.
US Pat. Appl. No. 20100056737 discloses a process of manufacturing high, very high, and ultra high molecular weight polymers comprising predominantly ethylene monomers. Ethylene is reacted in the presence of a catalyst system to produce a polymer having a viscosimetrically-determined molecular weight of at least 0.7×106 g/mol. The catalyst system generally includes a bridged metallocene catalyst compound, optionally with a co-catalyst.
Article titled “The synthesis and X-ray structure of a phenoxyimine catalyst tailored for living olefin polymerisation and the synthesis of ultra-high molecular weight polyethylene and atactic polypropylene” by Marc-Stephan Weiser et al. published in Journal of Organometallic Chemistry, 2006,691 (13), pp 2945-2952 reports synthesis of a phenoxyimine catalyst (bis-(N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride. The ligand as well as the complex have been fully characterised. An X-ray structure of the titanium complex was obtained. After activation with MAO, it was used as highly active catalyst in living olefin polymerisation of ethylene and propylene.
U.S. Pat. No. 6,369,177 discloses an olefin polymerization catalyst exhibiting excellent olefin polymerization activity and capable of producing polyolefins of excellent properties and to provide a process for olefin polymerization using this catalyst. The olefin polymerization catalyst comprises a transition metal imine compound (A) represented by the following formula (I-a) or (I-b) and at least one compound (B) selected from an organometallic compound (B-1), an organoaluminum oxy-compound (B-2) and a compound (B-3) which reacts with the transition metal imine compound (A) to form an ion pair;

PCT Appl. No. 2016005961 (IN2014MUM2267) discloses a heterogeneous single site catalyst immobilized on an inorganic oxide support and a method for the synthesis of the same using a step of generating a Schiff base imine ligand on the inorganic oxide support followed by lithiation and titanation. The use of the single site catalyst of the present disclosure is for polymerizing ethylene to obtain dis-entangled ultra-high molecular weight polyethylene. A method for immobilizing a single site catalyst on an inorganic oxide support, said method comprising the following steps: a. functionalizing said support by treating with a reagent to obtain a functionalized inorganic oxide support; b. treating said functionalized inorganic oxide support with a hydroxyl group containing aldehyde to obtain an inorganic oxide support with a Schiff base imine ligand; c. lithiating said inorganic oxide support with the Schiff base imine ligand with a lithiating agent to obtain an inorganic oxide support with a lithiated Schiff base imine ligand; and
d. treating said inorganic oxide support with the lithiated Schiff base imine ligand with a titanium halide to obtain said immobilized single site catalyst.
Article titled “Heterogeneity in the distribution of entanglement density during polymerization in disentangled ultrahigh molecular weight polyethylene” by Anurag Pandey et al. published in Macromolecules, 2011, 44 (12), pp 4952-4960 reports ethylene polymerization using [3-t-Bu-2-O—C6H3CHdN(C6F5)]2TiCl2 and MAO.
Article titled “FI catalyst for polymerization of olefin” by S. Damavandi et al. published in INTECH, 2012 reports FI catalysts can be synthesized by treating the phenoxy-imine ligands and transition metal halides to furnish FI catalysts.
Article titled “Influence of catalytic systems on the synthesis of (dis)entangled UHMWPE and its implications on mechanical properties” by Dario Romano published as thesis 2014 reports synthesis and characterisation of UHMWPE.
However, a drawback of such phenoxyimine-based catalysts is that the phenoxy group does not provide sufficient rigidity to prevent the resulting metallic complex from adopting different conformations leading to the presence of multiple catalytic sites. Furthermore, phenoxy groups only have a limited number of sites which can bear substituents, these being needed for tailoring and fine-tuning in order to increase catalytic activity and/or enhance the control over the UHMWPE microstructure (short-chain branching, long-chain branching etc).
Thus a new family of single-site catalysts are needed, which have ligands that are more rigid, are easier to fine-tune with a larger number of possible substituents but are also capable of preparing dis-UHMWPE. Accordingly, present inventors developed a novel olefin polymerization catalyst comprising iminesulfonate or iminecarboxylate ligands for the synthesis of disentangled ultrahigh molecular weight polyethylene (dis-UHMWPE) with improved physical and mechanical properties.